I have also used a kettle bell (or simply holding any weight will work) to sit in the bottom of a squat, centering the weight over one ankle at a time to slowly stretch the achilles.

This stretch, for sure. Press your knee forward past your toes while keeping your heel on the ground. I did this stretch a ton when I was younger, training for lower stances is kung fu, and I have no problem hitting the bottom of my squat positions even in barefoot shoes or chucks.